Marine craft such as high-speed racing boats undergo travel with respect to a body of water which involves both straight runs and 180 degree maneuvering turns. Such turns induce sideway skidding of boats provided with submerged hydrodynamic devices as well as a water surface piercing strut or skidplate through which skid opposing side forces are produced in an effort to avoid sideway skidding experienced at side slip angles of 35.degree. to 45.degree. resulting from centrifugal force produced during typical turning maneuvers. Large drag forces are imposed on the skidplates as well as the rudders by such maneuver activity, to reduce propeller thrust causing significant speed loss as the craft comes out of a turn.
Typical skidplates heretofore utilized had symmetric profiles on opposite sides thereof so as to avoid generation of side force during straight course run. To minimize drag resistance, the typical profiles of such skidplates were in the form of thin flat plates having a wedge formation at its leading edge. Although the use of camber section foils for such skidplates was considered, it was deemed unsuitable because of the large lift coefficient involved during straight line run at a zero angle of attack associated with generation of an undesirably large side force. Accordingly, it is an important object of the present invention to provide a skidplate having profile sections which perform like a camber foil to produce side force only when needed during turn maneuver, and yet perform like a symmetric foil during straight course run without reliance on corrective action of control devices.